Method and system for sampling at least one antenna

ABSTRACT

A method for testing at least one antenna having a receiver module and a coupling module which is arranged between the antenna and the receiver module. The antenna and the receiver module are supplied with a noise signal as a test signal by the coupling module. An instantaneous transmission coefficient, which indicates the ratio between a first noise signal (which is passed to the test module via a first path without passing through the at least one antenna) and a second noise signal (which is passed to the test module from the noise source via a second path which passes via the at least one antenna) being determined, and being compared with a reference transmission coefficient, which is stored in a transmission matrix, by a test module. An arrangement for carrying out the method is also provided.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method and an arrangement for testing atleast one antenna, in particular a multiple antenna system in a vehicle.

As the number of antennas on vehicles increases, it is becomingnecessary to carry out a functional test of the antenna system.Functional tests such as these are normally carried out in the removedstate. A functional test with the antenna in the installed state hasbeen particularly complex and required a particularly large amount ofeffort. For example, DE 196 18 333 A1 describes a circuit arrangementfor functional testing of mobile broadcast radio receiving systems inthe installed state. One disadvantage of this circuit arrangement isthat it has a calibrated signal generator to produce a test signal,which signal generator transmits a discrete test signal exclusively atthe frequency to which the receiver is tuned. Furthermore, the circuitarrangement is not suitable for diagnosis which accounts for externalinfluences, such as snow or ice.

A system for testing a signal transmitter/receiver, for example for areceiving antenna, is disclosed in U.S. Pat. No. 6,005,891. In thiscase, a pseudo-random noise signal source is used as the test signalsource. A complex circuit is used in the system to process a signalwhich has been reflected from a damaged receiving antenna and to comparethis with the original test signal. A correlation receiver, among otheritems, is required for this purpose. However, this system is highlycostly to produce, as a result of the use of the pseudo-random noisesignal source, which produces a high-speed digital signal, as well asthe correlation receiver. Furthermore, it is always necessary to knowthe level of the output signal from the pseudo-random noise signalsource.

The invention is thus based on a method for testing at least one antennain a vehicle, in which diagnosis can be carried out at all thefrequencies in one band, for example a radio, TV, mobile radio or ISMband, at low costs and in a particularly simple manner. Furthermore, theinvention provides a particularly simple arrangement for testing theantenna in the installed state. In the invention knowing the level ofthe test signal source is not necessary, thus making it possible to usea low-cost test signal source.

The advantages which are achieved by the invention are, in particular,that a noise signal from an uncalibrated noise source is injected intothe antenna as a test signal by means of a controllable coupling module.If there is only a single antenna, the noise signal which is beingreflected at the antenna input is evaluated as the received signal in atest module. For this purpose, the received signal is advantageouslyused to determine an instantaneous transmission coefficient, whichrepresents the relevant antenna, at a predetermined frequency or at twoor more frequencies in a band. The instantaneous transmissioncoefficient is compared with a reference transmission coefficient, whichrepresents the transmission behavior of the noise source via thecoupling module to the antenna and back to the receiver. A serviceableantenna produces minimal reflection at the antenna.

In the case of a multiple antenna system comprising two or moreantennas, the noise signal transmitted between the antennas is analyzedand assessed alternatively or in addition to the noise signal which hasbeen reflected at the respective antenna inputs. For this purpose, thenoise signal is injected into the antenna or antennas from theuncalibrated noise source or test signal source by means of a couplingcircuit, is received by an adjacent antenna, and is analyzed by means ofa transmission matrix in the test module, in particular in the receiver,for example an audio or video tuner. Such functional monitoring ordiagnosis using a simple uncalibrated noise source, which in thesimplest case is formed by a source in the receiver itself, allows aparticularly low-cost and simple arrangement. In particular, theproduction cost is particularly low. As a result of the use of alreadyexisting components in the receiver, the arrangement generally requireslittle space and, as a result of this and due to the integration of thetest module, for example, in a vehicle, there is no need for complextest transmitters at the end of the production line or for servicingwhen the diagnosis or test method is used in the vehicle field.

Furthermore, the use of a noise signal as the test signal allows adiagnosis covering all the frequency bands to be carried out on theantenna or antennas. In particular, a test such as this based on a noisesignal also allows evaluation relating to external influences on theserviceability of the antenna or antennas, such as snow or otherexternal interference signals, which lead to incorrect diagnosis in thecase of the conventional systems based on the prior art. In particular,this ensures that the antenna or antennas is or are tested and monitoredin the installed state as well, and thus, for example, while a vehicleis being driven.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention will be explained inmore detail in the following text in conjunction with the drawing, inwhich:

FIG. 1 shows, schematically, a circuit arrangement for testing theserviceability of a multiple antenna system,

FIG. 2 shows, schematically, the signal waveform of a test signal in themultiple antenna system,

FIGS. 3 to 5 show, schematically alternative embodiments of the circuitarrangement as shown in FIG. 1, with switchable transmission paths foran AM band and an FM band, and an FM band with diversity,

FIG. 6 shows, schematically, a flowchart of the test method, and

FIGS. 7 to 14 show, schematically, various circuit arrangements fortesting the serviceability of an individual antenna.

Mutually corresponding parts are provided with the same referencesymbols in all of the figures.

DETAILED DESCRIPTION

FIG. 1 shows a circuit arrangement 1 for testing an antenna system 4,which comprises two or more antennas 2, on a vehicle. The antenna system4 is integrated in a glass pane 6, for example the rear windshield, aside window, or the rear window and/or side window or windows of thevehicle. The circuit arrangement 1 has a receiver module 8 and acoupling module 10, which is arranged between the antennas 2 and thereceiver module 8. The antenna or coupling module 10 is used forinjection of a noise signal S into the respective antenna 2 and into thereceiver module 8, which is also referred to as a tuner. The receivermodule 8 also has a test module 12 for determination of an instantaneoustransmission coefficient (Ü_(vi)) on the basis of the ratio between thenoise signal component S′ that is injected via the antennas, and thenoise signal component S1 which is transmitted directly from the noisesource to the receiver. In order to determine the serviceability of therespective antenna 2, the test module 12 has a transmission matrix 14 inwhich a reference transmission coefficient (Ü_(vinorm)) (also referredto as (Ü_(vn-m))) is stored for the respective antenna 2, describing thetransmission response and/or transmission path. The serviceability ofthe antenna 2 is deduced from a comparison of the instantaneoustransmission coefficient (Ü_(vi)) with the reference transmissioncoefficient (Ü_(vinorm)). The coupling module 10, which is also referredto as an antenna module, has, as a diagnosis circuit 16, an uncalibratednoise source 18 and an RF switch 20 which can be driven. The noisesource 18 in this case covers all the frequency bands which can bedetected in the receiver module 8.

In one advantageous embodiment, the noise source 18 may be in the formof a bipolar transistor in an amplifier circuit. With the diagnosis ortest method proposed here, there is no need for a calibrated noisesource. This makes it possible to avoid the complex determination of theinstantaneous frequency response of the noise source 18, which isdependent on components and temperature. The RF switch 20 which can bedriven is, for example, in the form of switching diodes. The number ofswitching diodes corresponds to the number of antennas 2 which are usedas transmitting antennas 2(n) in the diagnosis mode. The number oftransmitting antennas 2(n) used governs the evaluation confidence of thediagnosis.

The diagnosis circuit does not involve expensive production costs butcan, for example, be accommodated on the board surface of the antennaamplifier module, by changing its layout. The data can be evaluated inthe tuner or receiver 8 by an addition to the software, and there is noneed for additional hardware. Depending on the nature and embodiment ofthe circuit arrangement 1, the receiver module 8 and the coupling module10 may be formed by a common module. Furthermore, the individual modulesmay be in the form of software and/or hardware, depending on thefunction. In addition, the arrangement and combination of the individualmodules may vary, depending on the requirement.

The switching diodes are driven by means of a digital counter 21. If thebit rate is low, a control signal DI transmits two voltage states fromthe receiver module 8 to the digital counter 21. The control signal DIcan be transmitted along an already existing RF cable in the same way asis already done for driving a given FM diversity circuit. The counter 21is switched onwards by one position on each positive edge of the controlsignal DI, so that all of the antenna branches A, B, . . . , Z areswitched through successively. Once the final antenna branch Z has beenswitched through and the diagnosis is produced, the next positive edgecauses the noise source 18 to be switched off or, alternatively, to beswitched to a state in which no antenna branch A to Z is switchedthrough. The next positive edge once again switches the first antennabranch A through in a new diagnosis cycle.

At least two rear windshield antennas 2 are successively connected astransmitting antennas 2(n) via the RF switch 20. In an antenna system 4having at least two antennas 2, the serviceability of the antennas 2 ispreferably measured by measurement of the near field transmissionbetween the antennas 2. The reference transmission coefficientsÜ_(vinorm) or factors for all the possible couplings between theantennas 2 form the transmission matrix 14. The instantaneoustransmission coefficients Ü_(vi) are determined analogously to this onthe basis of the transmission matrix 14, and are compared with thereference transmission coefficients Ü_(vinorm). In this case, theantennas 2 are used both as transmitting antennas and as receivingantennas.

The transmission path is determined by transmission of the noise signalS via one of the antennas 2 as a transmitting antenna n and by receptionof the received signal S′, which results from this, at one of the otherantennas 2 as a receiving antenna m, and by reflection of the noisesignal S at the antenna input of the relevant transmitting antenna n.

The evaluation on the basis of the transmission matrix 14 expedientlyallows identification of adverse affects, such as wetness, snow,external interference signals, which can affect two or more antennas 2.The test or diagnosis is carried out such that the transmission of thenoise signal S from the respectively selected transmitting antenna 2(n)to the other adjacent rear windshield antennas 2, which form thereceiving antennas 2(m), is tested in the receiver module 8, inparticular for all frequency bands. Each antenna 2 is thus tested forits transmission behavior Ü_(v) in a number of frequency bands. The FMband, the highest TV band and the AM band are expediently analyzed, sothat the operation of the antennas 2 can be tested and determinedreliably and easily on the basis of the transmission behavior Ü_(v).Since the transmission is further tested in different combinations oftransmitting antennas n and receiving antennas m, it is possible toexclude external fault sources.

During operation of the circuit arrangement 1, the RF switch 20 does notallow any noise signal S on the antenna path 22 during normal antennaoperation, when it is in the position 0. In the diagnosis or test mode,the RF switch 20 is switched successively to the positions 1 and 2, withthe noise signal S being injected successively in to the antenna path 22via coupling circuits 24, for example by means of T junctions orcapacitively. There, the noise signal S is split into the noise signalS1, which is passed directly from the noise source 18 to the tuner 8,and the noise signal S2, which migrates to the relevant antenna 2 and isemitted at the antenna 2. Statements relating to the serviceability ofthe relevant antennas 2 can be made from the comparison of the receivedsignal S2, which is received from the receiving antenna 2(m), with thenoise signal S1, which is supplied directly for level evaluation.Furthermore, depending on the extent of the analysis, amplifier andfilter circuits 26 which affect the transmission path and theirinfluence on the transmission can be taken into account. Since two ormore or all of the antennas 2 are used as transmitting antennas n, andall of the antennas 2 are used as receiving antennas m, the entiresystem can be represented by a transmission matrix 14 with a maximumsize of n×m.

The determination of the transmission matrix 14 for a level evaluationand the measurement tolerance to be expected will be described in thefollowing text with reference to FIG. 2. This is based on theassumption, by way of example, of a multiple antenna system 4 with threeantennas 2. However, the principle also applies to other systems 4 whichhave at least two antennas 2.

For level evaluation using the transmission matrix 14, the signal levelsSi1, Si2 and Si3 are respectively detected at the ports I, II and IIIfor level evaluation when two or more antennas i (i=1, 2, 3) are used asthe transmitting antenna n. In the case of an antenna system 4 which islargely completely serviceable, that is to say it is optimally matched,minimal reflection occurs at the antenna inputs 2. The noise signal Swhose level is Pr(f) is injected successively into each of the signalpaths 22 of the antennas 2. Some of the noise power is emitted via therespectively connected antenna 2, while a further portion is passed viathe respective filter amplifier circuit 26 in the path 22 directly tothe receiver module 8. The level Pr(f) of the noise source 18 need notbe known in advance before measurement, since it can be determined fromthe measurement evaluation by means of the test module 12 in thereceiver module 8. The measurement results in the diagnosis process arethus not dependent on the tolerance of the noise source 18.

The assumed transmission coefficient or reference transmissioncoefficient Ü_(vinorm)(f), the filter amplifier circuit 26 with thenarrowest tolerance δvi and the actual transmission coefficient on thebasis ofÜ _(vi)(f) where Ü _(vi)(f)=Ü _(vinorm)(f)×(1+δ_(vi)(f))  [1]are used as the basis for determination of the instantaneous noise powerP_(r).

The signal level S11, as detected in the level evaluation, for the firstantenna 2 at the port I in accordance withS ₁₁(f)=(P _(r)(f)/2)×Ü _(v1)(f)=(Pr(f)/2)×Ü_(v1norm)(f)×(1+δ_(v1)(f))  [2]is used as the basis for determination of the noise level P_(r)(f) for agiven measurement tolerance δ_(v):Pr(f)=2S ₁₁(f)/((Ü _(v1norm)(f))×(1+δ_(v1)(f))  [3]

Accordingly, the noise characteristics of the noise source 18 may differindividually for each component, may be dependent on the temperature,and need not be known in advance. This allows simple low-cost noisesources 18 to be produced. Once the noise level Pr(f) has beendetermined, the transmission coefficients Ü_(v2)(f) and Ü_(v3)(f) of theother filter amplifier circuits 26 can be determined from the respectivesignal levels S22 and S33.Ü _(v2)(f)=2S ₂₂(f)/P _(r)(f); Ü _(v3)(f)=2S ₃₃(f)/P _(r)(f)  [4]

By comparison with the reference transmission coefficients Ü_(v2norm)(f)and Ü_(v3norm)(f) or nominal values for the respective frequency bands,the serviceability of the respective filter amplifier circuit 26 caneasily be deduced from these coefficients Ü_(v2)(f) and Ü_(v3)(f). Thetolerance δv for the noise power Pr is also obtained from thesecoefficients Ü_(v2)(f) and Ü_(v3)(f). The transmission coefficientsÜ_(a12)(f) and Ü_(a13)(f) between the antennas 2 make it possible tocalibrate out the tolerances in the transmission path 28 on the basisthat:Ü _(a12)(f)=S ₁₂(f)/S ₂₂(f); Ü _(a13)(f)=S ₁₃(f)/S ₃₃(f)  [5]

The indication tolerance in the receiver 8 is not included in thisanalysis, since the assessment of the antenna system 4 always relates toits sensitivity. Accordingly, if the sensitivity of the receiver 8 ishigh, the antenna system 4 may have correspondingly poorer transmissioncharacteristics. The required quality of the antenna system 4 is thusalways assessed as a function of the available tuner sensitivity usingthe diagnosis system or the circuit arrangement 1, so that entiresystems 1 (receiver 8 and antenna system 4) with the same quality arealways assessed to be the same.

The transmission coefficients Ü_(a) not only provide information aboutthe serviceability of the antennas 2, but also about the extent to whichthe transmission path 28 between the antennas 2 is subject tointerference. If, for example, the antennas 2 are covered with snow,then all of the transmission coefficients Ü_(vi)(f) are interfered withto the same extent, and the diagnosis algorithm identifies that it isnot an antenna 2 which is faulty, but that all the transmission paths 28are affected. The state of the antennas 2, for example the fact that therear windshield 6 is covered with a foreign body, is deduced as afunction of the magnitude of the instantaneous determined transmissioncoefficients Ü_(vi)(f).

FIG. 3 shows an alternative embodiment of the circuit arrangement 1, inwhich, in order to test the various frequency bands of the receivermodule 8, the coupling module 16 is intended to inject the noise signalS into the relevant transmission branch 30 or 32 for the FM band or AMband, respectively, using the positions 1 and 2 of the RF switch 20. Thecircuit arrangement 1 in this embodiment has a two-antenna system 4 forthe AM and FM bands. FIG. 4 shows a further embodiment of the circuitarrangement 1 for a five-antenna system 4 for the AM band and the FMband, with quadruple diversity. The number of positions of the RF switch20 must be increased by the appropriate number of antennas in order totest the FM band with diversity. The test procedure is carried out asalready described above. Accordingly, the noise signal S from the noisesourse 18 is injected separately into each antenna 2 by means of the RFswitch 20. Relevant transmission coefficients Ü_(vi)(f) are determinedfor all possible combinations of the antennas 2 on the basis of therespective received signal S′, which is received by means of one of theadjacent antennas 2, and the transmitted noise signal S, and is comparedwith the reference transmission coefficients Ü_(vinorm)(f) for thetransmission matrix 14.

The method described above for testing the serviceability of the antenna2 is not dependent on the antenna type. FIG. 5 shows one embodiment fora further diagnosis circuit for a five-antenna system 4, for a so-calledhigh-end version for AM, FM and TV diversity. As is illustrated in FIG.5, it is also, by way of example, possible to investigate an FZV antenna36 (FZV=radio central locking) on the basis of the method describedabove, if the associated FZV receiver 38 is connected to the AM/FM tuner8 via a data line 40, so that information about the received level istransmitted to the AM/FM receiver 8 for evaluation.

Alternatively or additionally, depending on the equipment fitted to thevehicle, it is also possible to investigate the serviceability of mobiletelephone and/or GPS antennas via broadband coupling to TV, AM and FMantennas. In this case, it is irrelevant where and how the individualantennas 2 are integrated in the vehicle.

During operation of the circuit arrangement 1, as shown in one of theFIGS. 1 to 5, the total of n antennas 2 are successively connected astransmitting antennas. Depending on the number n of transmittingantennas 2, this results in a corresponding number m of receivingantennas 2, and thus in n×m level information items, which arepreferably in the form of a level or transmission matrix 14, in order torepresent the transmission behavior Ü_(v). A permissible value range canbe produced for each transmission coefficient Ü_(vi) in the transmissionmatrix 14, which:

-   -   1. is individually associated with the coupling of in each case        one antenna pair 2(n, m), and    -   2. is dependent on all of the instantaneous measured        transmission coefficients Ü_(vi) in the transmission matrix 14.

If a permissible value range is exceeded, one or more antennas 2 is orare determined to be defective on the basis of the transmission matrix14.

External interference effects, which affect one or more antennas 2, forexample ice on the rear windshield 6, are advantageously analyzed andidentified in the diagnosis process by dynamically matching the valueranges to the instantaneous reception situation.

Table 1, below, shows one example of a transmission matrix 14 for anantenna system 4 with four antennas 2. TABLE 1 TX/RX Ant 1 Ant 2 Ant 3Ant 4 Ant m Ant 1 P11 P12 P13 P14 . Ant 2 P21 P22 P23 P24 . Ant 3 P31P32 P33 P34 . Ant 4 P41 P42 P43 P44 . Ant n . . . . Pnmwhere Ant n=the number of transmitting antennas, Ant m=the number ofreceiving antennas, TX=a transmitter, RX=a receiver, Pnm=the signallevel.

Depending on the nature and the function of the circuit arrangement 1,the transmission matrix 14 has, as information items, level and/orfrequency values which represent the reference transmission coefficientsÜ_(vinorm) and/or instantaneous transmission coefficients Ü_(vi) for therelevant antenna combination. During a diagnosis, the instantaneoustransmission coefficients Ü_(vi) are compared with the referencetransmission coefficients Ü_(vinorm) for each of the antennacombinations 2(n, m). To do this, the transmission matrix 14 must beinitialized, for example before initial use of the vehicle, such as atthe time of production. Reference knowledge is generated for thispurpose, on the basis of which a diagnosis can then take place. Onepossible method for knowledge generation and evaluation is described inthe following text.

A diagnosis is carried out in a number of steps:

-   -   I) symptom generation    -   (for example on the basis of the available information in the        transmission matrix 14)    -   II) fault identification    -   III) fault localization

By way of example, FIG. 6 shows a flowchart for the diagnosis method,comprising the following steps:

-   (1) Recording of the matrix elements, for example on the basis of    measurements, presetting type-specific values or reading stored    previous values;-   (2) Calibration by normalization of the matrix elements with respect    to the transmission power and transmission losses. The calibration    is carried out on the basis of the element on the diagonal of the    transmission matrix 14.-   (3) Identification of “invalid states”, such as an icy rear    windshield or an electromagnetic field which is subject to severe    interference.-   (4) Evaluation by comparison with stored fault situations or by    means of a decision network. Alternatively or additionally, a fault    in one or more of the antennas 2 or antenna combinations 2(n, m) can    be identified on the basis of a frequency analysis or amplitude    analysis.-   (5) Filtering, plausibility check, that is to say the diagnosis    process is carried out n-times. Depending on the requirement, a    fault message is emitted only after a fault situation has been    successfully detected n-times, otherwise no message is produced or a    “healthy” message is emitted, that is to say the fault memory is    reset when the satisfactory state is identified two or more times.

The measurement and diagnosis method will be explained in the followingtext with a reference to an example. The transmission behavior betweendifferent rear windshield antennas 2 in their near field is determinedby means of a so-called network analyzer. The transmission behavior ismeasured by injecting the noise signal S into the antennas 2successively. The vehicle roof, the C pillars and the rear cover withsheet steel parts electrically connected has been modeled in order toestimate the field behavior on the actual vehicle. Measurements havebeen carried out for intact antennas 2 as well as for defective antennas2, for example for a discontinuity in the windowpane contacts and/or fora discontinuity in the antenna wires on the rear windshield 6. Theinfluence of wetness on the transmission behavior has also beenmeasured.

The transmission or noise signal S was injected directly into theantenna 2, with the antenna amplifier disconnected. The transmittingantenna 2 is thus not matched. If the transmitting antenna 2 is fed in amatched manner, the transmission factors are better. The values includedin the following tables are the S21 transmission coefficients in dB, ineach case measured at 100 MHz (FM). S21 transmission coefficientsrepresent the transmission factor or transmission coefficients Ü_(vi)between the respective antennas 2 which are coupled via the near field.In addition to the normal situation in which the antennas 2 areserviceable, a number of types of fault situations, and their influenceon the transmission factors, have been investigated. The faultsituations were brought about by disconnecting the windowpane contacts,interrupting the windowpane antenna wires, influencing the near field ofthe antennas 2 by means of water on the windowpane, and by means ofmetal surfaces located in the near field of the antennas 2.

For the normal situation without any fault influence on an antennasystem 4 which comprises six antennas 2 and is integrated in the rearwindshield 6, the transmission matrix illustrated in Table 2 is obtainedfor the frequency f=100 MHz (FM band): TABLE 2 FM1/ dB TV1 FM2/TV2 TV3FM4/TV4 AM FZV FM1/TV1 X −25.21 −22.37 −19.25 −22.17 −24.76 FM2/TV2 X−9.195 −22.51 −8.053 −5.906 TV3 X −14.56 −19.12 FM4/TV4 X −23.38 −23.74AM X −2.456 FZV X

The instantaneous transmission coefficients Ü_(vi) determined by meansof the transmission matrix 14 are all better than −25 dB and therequired transmission powers to be expected for near field transmissionare very low, measured with respect to the conventional far fieldtransmission/reception situation.

In order to illustrate the detection of poor contacts with the antenna2, the window pane contacts were made worse or were interrupted at theconnections to the antennas FM1 and TV3 by the insertion of layers ofpaper of different thickness. As is shown in Table 2, the antennacombination FM1 and TV3 normally has a transmission coefficient Ü_(vi)of −22.37 dB.

Table 3 shows the influence of poor contacts on the transmissionbehavior in the form of a significant change in the transmissioncoefficients Ü_(vi) determined in this instance by means of thetransmission matrix 14. TABLE 3 Fault situations S_(TV3→FM1) in dB for100 MHz Normal situation −22.37 1 leaf on FM1 −25.26 1 leaf on TV3−41.29 20 leaves on FM1 −41.03 20 leaves on TV3 −61.19 20 leaves on bothFM1 and TV3 −67.41 Metal sheet in front of the −19.42 windowpane

The final fault situation “metal sheet in front of the windowpane” inthis case simulates an invalid state, as would occur, for example, as aresult of conductive material such as ice or water on the rearwindshield 6.

Furthermore, a discontinuity in the antenna wires as modeled, forexample by cutting through the conductor track for the antenna TV3 orcutting through both conductor tracks for the antennas TV3 and FM2. Inthis case, the test or noise signal S is transmitted via the antenna FM2or FM1, depending on the drive for the coupling or RF switch 20. Thetransmission coefficients Ü determined by means of the transmissionmatrix 14 are shown in the following Tables 4A to 4C. TABLE 4A FM2 → TV3(dB) 100 MHz 800 MHz Normal situation −9.195 −32.10 Fault on antenna TV3−8.620 −38.50 Fault on antenna TV3 −13.53 −29.43 and FM2

TABLE 4B FM1 → FM2 (dB) 100 MHz 800 MHz Normal situation −25.21 −37.81Fault on antenna FM2 −32.57 −27.03

TABLE 4C FM2 → FM4 (dB) 100 MHz 800 MHz Normal situation −22.51 −33.23Fault on antenna FM2 −32.07 −28.70

All the fault situations can clearly be identified from a decrease orincrease in the transmission factors Ü. The method described above thusallows the serviceability of individual antennas 2 to be diagnosedparticularly easily and reliably. Further transmission characteristicsor operating parameters may be taken into account, depending on the typeof antenna. For example, the rise in the so-called cross-coupling factorS FM1→FM3 in the UHF band (800 MHz) in the event of a fault in the FMantenna can be explained by shortening of the electrically effectiveantenna length. In contrast, the same fault in the FM band leads to acorresponding reduction in the coupling.

In a further test of the antennas 2, they are analyzed for changescaused by the influence of water on the rear windshield 6, or by otherobjects in the vicinity of the rear windshield 6. As is shown in theTables 5A and 5B, water spray has virtually no influence on thetransmission behavior at 100 MHz. In contrast, if objects, in particularconductive objects, are arranged closely in front of the rear windshield6, these changes are indicated in the diagnosis, since they represent asignificant influence on the transmission behavior of individual antennapairs. TABLE 5A FM2 → FM4 (dB) 100 MHz 800 MHz Normal situation −22.51−33.23 Metal sheet in front of −30.23 −29.20 the windowpane Wetwindowpane −22.09 −26.91

TABLE 5B FM2 → TV3 (dB) 100 MHz 800 MHz Normal situation −9.195 −28.50Metal sheet in front of −9.159 −29.00 the windowpane Thick plastic filmon −8.330 −30.45 the windowpane

FIG. 7 illustrates an alternative embodiment of the circuit arrangement1. The circuit arrangement 1 is designed for a single antenna system 4.In this case, instead of evaluating the noise signal S which istransmitted from the transmitting antenna to the receiving antenna 2, anoise signal S₂ which has been reflected at the relevant antenna input42 of the single antenna 2 is analyzed and assessed on the basis of thetransmitted noise signal S₁. Since any damage to the antenna 2 adverselyaffects its matching, reflections are produced at its input 42. When theRF switch 20 is in the position 0, it does not allow any noise signal Sto pass from the noise source 18 to the antenna path 22 during normalantenna operation. RF switch 20 is in the position 1 in the diagnosismode. The noise signal S is then coupled via a coupling network 24, forexample a T element, into the antenna path 22, where the noise signal Sis split into the noise signal S₁, which is passed directly from thenoise source 18 to the receiver module 8, and the noise signal S₂, whichmigrates to the antenna 2 and is reflected at the antenna 2.

The superimposition of the noise signals S₁ and S₂, comprising the noisesignal S₁ that is passed directly from the noise source 18 to thereceiver 8, and the reflected noise signal S₂, results in acharacteristic frequency characteristic with notches, from whichconclusions are drawn about the state of the antenna 2, and these areassessed. However, this is dependent on a calibrated noise source 18,whose frequency characteristic is known. The serviceability of theantennas 2 can be determined only by comparison of the frequencycharacteristic of the superimposition of the noise signals S₁ and S₂with the frequency characteristic of the noise signal S₁.

In order to allow the calibrated noise source 18 to be replaced by alower-cost uncalibrated noise source 18, the static coupling circuit 24has a switching function added to it, with additional positions 2 and 3for the switchable coupling circuit 44, as is illustrated in FIG. 8. Inthe switch position 2, the noise signal S1 is passed directly to thereceiver 8, where it is detected. This means that the antenna path 22 isopen. The frequency characteristic of the instantaneous noise signal S1is then known and is stored for level evaluation. The position 3 is thenselected by means of the switchable coupling circuit 44, so that theantenna path 22 is closed. The frequency characteristic of thesuperimposition of the noise signals S1 and S2 is now detected in thelevel evaluation on the basis of the transmission matrix 14, and iscompared with the frequency characteristic of the stored noise signalS1.

As an alternative to the switchable coupling circuit 44 or to the openswitch, a superimposition of the noise signal S1 and of the noise signalS2 as reflected on a defined impedance Z can also be measured andanalyzed for the reference measurement of the noise signal S1, with acalculation then being carried out back to the frequency characteristicof the pure noise signal S. The associated circuit arrangement 1 isillustrated, by way of example, in FIG. 9.

The frequency characteristic of the illustrated embodiments in FIGS. 7to 9 for single antenna systems 4 is detected and analyzed in arelatively wide frequency band, in order to ensure statements that areas good as possible about the serviceability of the antenna 2, sincesignificant level changes do not necessarily occur in the area of themid-frequency fm in the superimposed noise signal S1+S2 if the antenna 2is damaged.

A directional coupling circuit 46, for example a directional coupler, asis illustrated in FIG. 10, is preferably used in order to allow theserviceability of the antenna 2 to be deduced just from the levelchanges of the reflected signal S2 when a narrow frequency band f isanalyzed. In this case, only the reflected signal S2 is detected, whoselevel is considerably lower than the noise signal S1 if the antenna 2 isfunctioning. The level evaluation is in this case dependent on the noisesignal level S1 already being known. This embodiment requires acalibrated noise source 18.

In order to allow a low-cost uncalibrated noise source 18 to be used, adirectional coupling network 48 with a switchable signal flow directionis used, as is illustrated in FIG. 11. By way of example, a directionalcoupler with alternatively switchable inputs E1, E2 is provided for thispurpose. In the switch position 1, the noise signal S is passed via thedirectional coupler 48 to the antenna 2, is reflected and is detected asa signal S2 in the level evaluation. In the switch position 2, the noisesignal S is passed via the directional coupler 48 directly to the levelevaluation, where it is detected as a reference signal S1.

FIGS. 12 to 14 now show modified forms of the arrangement shown in FIG.11, in which diagnosis is likewise possible using an uncalibrated,low-cost noise source 18. In this case, uncalibrated always means thatthe transmission power of the noise source is not known, and it need notassume reproducible values so that, for example, a major temperaturedrift in the transmission power is permissible. Only the design andfunction differences in comparison to FIG. 11 will be explained in moredetail for these embodiments in the following text.

The embodiment shown in FIG. 12 uses a directional coupling network 50with a switchable signal flow direction, in order to make it possible touse a low-cost uncalibrated noise source. A directional coupler withalternatively switchable inputs is likewise used in this case, as in theembodiment shown in FIG. 11 and in the embodiment shown in FIG. 12.However, in contrast to FIG. 11, one input is terminated with a 50 Ωimpedance. In addition, the embodiment shown in FIG. 12, in contrast tothe embodiment shown in FIG. 11, has a modified filter amplifier circuit26′ with a switchable amplifier. Furthermore, a switch 49 is alsoprovided and is used in conjunction with the switchable amplifier forswitching from the signal path from the noise source 18 via the antenna2 to the receiver 8 to the signal path from the noise source 18 directlyto the receiver 8, and vice versa. In the switch position 2, the noisesignal S from the noise source 18 is passed via the directional coupler50 directly to the level evaluation, where it is detected as a referencesignal S1, in order to make it possible to determine and calibrate outthe noise level. For direct measurement of the noise signal S, theswitchable amplifier 26′ is switched off, that is to say it is switchedto the switch position 4, in order to interrupt the signal path via theantenna 2 to the receiver 8. In addition, an attenuator DG can beinserted into the path, to provide any required level reduction. In theswitch positions 3 and 5, the noise signal S is passed to the antenna 2,where it is reflected and is passed via the modified filter circuit 26′in the antenna module 10 to the receiver 8, in which it is detected inthe level evaluation as a signal S2. The operation of the modifiedfilter circuit 26′ can thus also be checked, in addition to that of theantenna 2. When the RF switch 20 is in the switch position 0, the noisesource 18 is switched off, for normal operation.

FIG. 13 shows a modified form of the embodiment shown in FIG. 12, whichcan be used when it is not possible to use the modified filter circuit26′ with a switchable amplifier, but only the filter circuit shown inFIG. 11. In this case, an additional switch 51 with switch positions 4′and 5′ is provided, by means of which the switch positions 4 and 5,which are provided in the switchable amplifier in the modified filtercircuit 26′ in FIG. 12, are replaced. The use of this additional switchallows the same function to be achieved as that described in conjunctionwith FIG. 12.

As a result of the use of this additional switch 51, it is now alsopossible to dispense with the RF switch 20. The resulting circuit isillustrated in FIG. 14. In this embodiment, the RF switch 20 is nolonger required to switch off the noise source 18, since it can now beswitched off by a combination of the switch positions 3 and 4.

The advantages which are achieved by the invention are, in particular,that it is possible to use a noise generator 18 which can be integratedin the antenna module 10 as a transmitter. The tuner or transceiver,which has being switched to a diagnosis mode, can be used as thereceiver 8. This results in a particularly low-cost transmitter. Sincethe receiver 8 already exists, software can be added to it for thediagnosis function.

As a further alternative embodiment of the invention, an additionalantenna can be provided which, in contrast to the antenna 2, is notconnected to the receiver module 8. The noise signal S is now injectedinto this additional antenna from the noise generator 18. The additionalantenna then transmits this noise signal to the antenna or antennas 2.The respective received signal S′ or S2 which results from this isreceived and evaluated by the test module 12 in the receiver module 8.

As described above, the present invention discloses the use of a verysimple low-cost test signal source for antenna diagnosis. This isachieved by using an economically advantageous low-price noise signalsource whose power need not be known. The noise source is suitable fortesting antennas in a number of frequency bands, for example AM, FM, TV,owing to its wide signal spectrum. The sequential use of a differentantenna in each case as the transmitting antenna makes it possible toproduce a transmission matrix which represents the near-field couplingbetween different antenna combinations. The signal power of the noisesource or test signal source can be calibrated out by means of thistransmission matrix. Accordingly, it is possible to use a simple,low-cost test signal source whose level, in contrast to all previousapproaches, need not be known and need not be reproducible. Thetransmission matrix is additionally used to calculate out externalinfluences which affect all or two or more of the antennas, such as anice, snow or fallen-leaf coating on them all, as well as externalinterference signals. A directional coupler in a calibration circuit isused for an arrangement for single antenna systems. In this case, thereception level is measured for each of two or more switch positions inthe arrangement at the tuner. The power of the low-price signal sourcecan be determined and calibrated out from different level values. Thiscalibration circuit may, of course, also be used for two or moreantennas.

In summary, the present invention discloses a method for testing atleast one antenna 2 having a receiver module 8 and a coupling module 16which is arranged between the antenna 2 and the receiver module 8. Inthis case, the antenna 2 and the receiver module 8 are supplied with anoise signal S as a test signal, by means of the coupling module 16. Aninstantaneous transmission coefficient is then determined by means of atest module 12 on the basis of a superimposition of the noise signal S,S1 with a received signal S′, S2 which results from the noise signal, S,S1, and is compared with a reference transmission coefficient which isstored in a transmission matrix. Furthermore, an arrangement is likewisedisclosed for carrying out the method according to the invention.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1-22. (canceled)
 23. A method for testing at least one antenna using areceiver module and a coupling module, the coupling module is arrangedbetween the at least one antenna and the receiver module, in which theantenna and the receiver module are supplied by the coupling module witha noise signal from at least one noise signal source as a test signal,the method comprising the acts of: determining an instantaneoustransmission coefficient which indicates the ratio between a first andsecond noise signal, the first noise signal is passed to the test modulevia a first path without passing through the at least one antenna, andthe second noise signal is passed to the test module from the noisesource via a second path which passes via the at least one antenna; andcomparing the instantaneous transmission coefficient with a referencetransmission coefficient, which is stored in a transmission matrix, by atest module.
 24. The method as claimed in claim 23, wherein the at leastone noise source is an uncalibrated noise source.
 25. The method asclaimed in claim 24, wherein switching takes place between the firstpath and the second path using a switchable coupling circuit whichinjects the noise signal into the first and second paths respectively,such that the noise signal is passed directly to the receiver via thefirst path, while a noise signal which has been reflected from the atleast one antenna is superimposed on the noise signal and is passed tothe receiver via the second path, and the second noise signal isdetected on the basis of the transmission matrix, and is compared withthe frequency characteristic of the first noise signal.
 26. The methodas claimed in claim 24, wherein a switchable coupling circuit, whichinjects the noise signal into the first and second paths, and in whichthe noise signal which is reflected at the at least one antenna has thenoise signal superimposed on it on an impedance, switches between thefirst path and the second path such that the noise signal is passeddirectly to the receiver via the first path, while a noise signal whichhas been reflected from the at least one antenna is superimposed on thenoise signal and is passed to the receiver via the second path, and thesecond noise signal is detected on the basis of the transmission matrix,and is compared with the frequency characteristic of the first noisesignal.
 27. The method as claimed in claim 24, wherein a directionalcoupling network with a switchable signal flow direction, which injectsthe noise signal into the first path or second path, switches betweenthe first path and the second path such that the noise signal from thenoise source is made available as the first noise signal, and the noisesignal, which is being reflected on the antenna is made available as thesecond noise signal, for evaluation at the receiver.
 28. The method asclaimed in claim 27, wherein the switching between the first path andthe second path is carried out using an additional switching device inthe first path and a switchable amplifier in the second path, instead ofbeing carried out at the inputs of the directional coupling network. 29.The method as claimed in claim 23, wherein a calibrated noise sourcewhose frequency characteristic is known is used as the at least onenoise source, a superimposition of the first and second noise signals issupplied to the test module and is in the form of a typical frequencycharacteristic, and the typical frequency characteristic is comparedwith the known frequency characteristic of the calibrated noise source.30. The method as claimed in claim 23, wherein an additional antennawhich has no connection for the receiver module and into which the noisesignal is injected, sends this noise signal as a test signal to the atleast one antenna.
 31. The method as claimed in claim 23, wherein the atleast one antenna is part of a multiple antenna system which has two ormore antennas, and a noise signal which been reflected at each of theindividual antennas, and/or a noise signal which has been transmittedbetween the antennas are/is evaluated as the second noise signal. 32.The method as claimed in claim 23, wherein the transmission coefficientand the reference transmission coefficient are determined by a frequencyanalysis and/or level analysis.
 33. An arrangement for testing at leastone antenna, the arrangement comprising: a receiver module; a couplingmodule which is arranged between the at least one antenna and thereceiver module, wherein the coupling module injects a noise signal fromat least one noise source into the at least one antenna and into thereceiver module; and a test module which determines an instantaneoustransmission coefficient, which indicates the ratio between a first andsecond noise signal, the first noise signal is passed to the test modulevia a first path without passing through the at least one antenna, andthe second noise signal is passed to the test module from the noisesource via a second path which passes via the at least one antenna, andwhich compares the instantaneous transmission coefficient with areference transmission coefficient which is stored in a transmissionmatrix.
 34. The arrangement as claimed in claim 33, wherein the at leastone noise source is an uncalibrated noise source.
 35. The arrangement asclaimed in claim 34, further comprising: a switchable coupling circuitwhich injects the noise signal into the first and/or second path, whichswitches between the first path and the second path, such that noisesignal can be supplied directly to the receiver via the first path whilethe noise signal which is being reflected from the at least one antennaand is superimposed on the noise signal can be supplied to the receivervia the second path, the test module detecting the second noise signalon the basis of the transmission matrix, and comparing it with thefrequency characteristic of the first noise signal.
 36. The arrangementas claimed in claim 34, further comprising: a switchable couplingcircuit which injects the noise signal into the first or second path andin which the noise signal which has been reflected at the at least oneantenna can be superimposed on the noise signal in an impedance, whichswitches between the noise signal is supplied directly to the receivervia the first path while the noise signal which is being reflected fromthe at least one antenna and is superimposed on the noise signal issupplied to the receiver via the second path, the test module detectingthe second noise signal on the basis of the transmission matrix, andcomparing it with the frequency characteristic of the first noisesignal.
 37. The arrangement as claimed in claim 34, further comprising:a directional coupling network with a switchable signal flow direction,which injects the noise signal into the first or second path, whichswitches between the first path and the second path, such that the noisesignal from the noise source is made available as the first noisesignal, and the noise signal, which is being reflected on the antenna ismade available as the second noise signal, for evaluation at the testmodule.
 38. The arrangement as claimed in claim 37, wherein anadditional switching device is in the first path and a switchableamplifier is in the second path, by means of which it is possible toswitch between the first path and the second path instead of to theinputs of the directional coupling network.
 39. The arrangement asclaimed in claim 33, wherein the at least one noise source is acalibrated noise source whose frequency characteristic is known.
 40. Thearrangement as claimed in claim 39, wherein the noise signal can beinjected by a coupling network into the path from the at least oneantenna to the test module, such that the first and the second noisesignal are superimposed, with the superimposition resulting in a typicalfrequency characteristic, and in which the test module compares thetypical frequency characteristic with the known frequency characteristicof the calibrated noise source.
 41. The arrangement as claimed in claim39, wherein the noise signal is injected by a directional couplingcircuit into the path from the at least one antenna to the test module,such that only the second noise signal is detected, and the test modulecompares the typical frequency characteristic resulting from the secondnoise signal with the known frequency characteristic of the calibratednoise source.
 42. The arrangement as claimed in claim 33, furthercomprising: an additional antenna which has no connection for thereceiver module, which sends the noise signal as a test signal to the atleast one antenna, with the coupling module injecting the noise signalinto the additional antenna.
 43. The arrangement as claimed in of claims33, wherein the coupling module has at least one RF switch forconnection of the at least one antenna.
 44. The arrangement as claimedin claim 33, wherein the transmission matrix in the case of a multipleantenna system, comprises a number of transmitting antennas andreceiving antennas as antenna pairs which correspond to the number ofantennas.